The present invention is directed to the fabrication and structure of head sliders for use in storage devices, such as hard disk drives (HDDs), and in particular the provision and usage of electrical bond pads on a slider surface structure to accommodate needs of slider design and fabrication process as well as slider operation within a disk drive.
Head sliders (sliders, for short) are fabricated for utilization within HDDs for positioning a magnetic head including, e.g., read and write elements, relative to one or more spinning disks. Each slider typically includes read elements and write elements along with electrical contacts to facilitate electrical connection with an electronic data control system. Sliders are also provided with air bearing features that controllably guide the manner by which the slider flies at a “fly height” on an air bearing created by a spinning disk. Specifically, the aerodynamic properties of the slider topography influence the fly height, pitch, roll, and other important features of the slider. These features of the slider range in size from nanometer size to millimeter size. Sliders may also include writers, read elements (e.g., readers), and/or reader-heaters used to modulate the distance of the slider from a magnetic disk contained in an HDD by using thermal expansion properties of the materials that compose the slider.
Typically, a separation distance between the slider, which contains the read and write elements (e.g., transducers) and the air bearing features, and a spinning magnetic disk is ten nanometers (nm) or less. The separation distance in this context is generally referred to as a fly height. In order to improve reading areal density, it is generally desirable to reduce the separation distance. One way to increase performance and to allow for smaller separation distance is to better flatten or reduce the roughness or imperfections of certain of the slider element surfaces, namely the air bearing surface (ABS). Moreover, smaller and smaller sliders are being designed to fly closer to the disk, and more and more electronic functionality is desired.
The fabrication process of a slider includes a multitude of steps involving a high level of complexity, low tolerances, and small size specifications. Typical process steps include fine line photolithography, reactive ion etching, ion milling, and thin film deposition. The sliders may include a substrate portion, an insulator layer, and a multilayer thin film portion that includes various operative layers and elements of the slider, such as read and write transducers, heater elements, laser elements, and others, as are known and developed. The sliders are generally fabricated utilizing well-known wafer build techniques.
An important slider fabrication process step is a plate lapping step that is used to ensure that the surface roughness of the slider ABS is minimal. Plate lapping is a machining process that uses an abrasive material to wear away, flatten, and/or smoothen a surface. Materials used in the manufacturing of a slider vary depending on the desired properties. Typically, magnetic recording heads are constructed from a variety of materials; e.g., magnetic alloys, metal conductors, ceramic and polymer insulators in a complex three dimensional structure with precise tolerances.
Sliders are fabricated from wafers that are created based upon the materials and layers specified for a desired slider construction. From such a wafer, a chunk or portion of the wafer is separated from the rest, which portion is typically dimensioned based upon a desired number of rows and number of sliders in each row. The wafer portion is sliced into the number of rows provided, creating an equal number of slider bars as there are rows.
In the form of slider bars, a collective slider bar ABS is generally lapped for sizing the sliders, while increasing surface flatness and decreasing surface roughness. The ABS of each slider may be lapped to comply with desired surface standards. After lapping, the individual sliders can be diced from one another.
In order to monitor the progress of a lapping operation, an electrical method has been developed utilizing electrical lapping guides (ELGs) as provided within the layered structure for each slider. By many developed electrical processes, electrical resistance is typically measured across bond pads (e.g., terminals or poles) as bond pad pairs that are electrically connected with the ELGs within the slider. These bond pads are known as ELG pads. The ELG pads are typically located on the slider trailing edge (TE) along with other bond pads that are provided for electrical device functionality of the many devices of recently developed slider designs. Not only is there becoming greater desire for more device bond pads, but less area for these bond pads may be available as sliders continue to shrink in size to accommodate higher density of data storage and smaller form-factor HDDs.
ELG pads are generally positioned to be electrically accessed on the slider TE and so that as the slider air bearing surface is reduced by lapping or otherwise, a width of the ELGs is reduced. As the ELGs are reduced in width, a measure of resistivity across the ELG pads increases until a determined value is reached, or until the circuit becomes open.
In various slider designs, ELG pads may take up approximately the lower half of the TE of each slider. The device bond pads are typically fully located within the upper half region of the slider TE. Moreover, the ELG pads are often sized for electrical connection, such as by a mechanical wire bonding process (using, e.g., gold wire), so that they can be temporarily electrically connected to the ELG bond pads for resistance monitoring during the lapping process and then removed from the ELG bond pads. Such mechanical wire bonding, as a general matter, requires greater bond surface area than the electrical bond pads for device functionality, which can utilize other developed solder techniques with smaller wires and/or flexible circuit terminals. After wafer and slider processing is complete, there is often no further functionality of the ELG pads. The ELG pads remain on the surface of the slider TE, but are generally inactive during operation of an HDD.
As the ELG pads typically occupy a significant amount of the available surface area of the TE of the slider, paired with a concurrent need for increased quantity of devices and functionality, a shortage of space for additional bond pads can lead to a desire to make better or more efficient use of existing bond pads and available slider surface area in general.